Firelogs were invented in America in the 1970's by mixing sawdust with petroleum waxes. Originally a typical firelog weighed 2 to 2.5 kg, and burned for around 3 to 4 hours. Firelogs are very convenient. Since they burn for so long it is not necessary to regularly feed the fire with further fuel, as would be the case with regular fuel such as wood or coal. Firelogs typically are sold in packaging that itself can be lit, which makes them extremely clean and easy to burn and to store.
In recent years, the sharp increase in the costs of petroleum wax has led to the use of non-petroleum waxes, either alone or in addition to petroleum waxes. EP2104727 discloses an artificial firelog using non-petroleum waxes. EP2108034 discloses alternative fibre materials to sawdust, including agricultural by-products.
Firelogs such as those disclosed in EP2108034 and EP2104727 are made by heating the wax so that it is liquid and mixing it with the sawdust, or other cellulosic fibre. The mixture of fibre and wax is then cooled and formed into a firelog, typically by extrusion, moulding or compression. Extrusion is by far the most preferred method for the manufacture of firelogs, since it is much more economical to use a continuous extrusion method, than a moulding or compression method which is not continuous. In order to ensure that the mixture of wax and fibre can be formed into a firelog, it is necessary that the wax has certain properties. In particular, the wax must act as a binder to hold the fibres together in the firelog.
With the current climate of increasing environmental awareness, there is mounting pressure on fuel manufacturers to make their products as environmentally sound as possible. In the UK many built up areas, such as the City of London, are subject to strict regulations that all fuel burnt in these areas must meet. In particular, the Clean Air Act 1993, together with Regulations and Orders made under the Act, provide the current legislative control. Under this Act, Local Authorities may declare the whole or part of a district to be a Smoke Controlled Area. It is an offence to emit smoke from a chimney of a building, furnace or any fixed boiler in a designated Smoke Controlled area. Fuels can be authorised by a Statutory Instrument and currently authorised fuels include inherently smokeless fuels such as gas, electricity and anthracite, together with specific brands of manufactured solid smokeless fuels. These fuels have to pass tests to confirm that they are capable of burning in an open fireplace while producing smoke emissions of less than 5 grams per hour. In America, there is a similar test regulated by the EPA. The EPA test relates to the appliance rather than the fuel and sets a mandatory smoke emission limit for wood stoves of 7.5 grams per hour for non-catalytic stoves and 4.1 grams per hour for catalytic stoves. Throughout Europe and the rest of the world, similar regulations apply.
Saturated waxes in general are known to burn more completely, and in a much cleaner manner, than unsaturated waxes. As noted above, it is desirable to use non-petroleum waxes. However, non-petroleum saturated waxes, such as fatty triglycerides, fatty acid, fatty alcohol, fatty esters, are typically solid at room temperature and can be brittle. This means that using conventional manufacturing methods for firelogs, it is not generally possible to use 100% saturated non-petroleum waxes, as they are not sufficiently plastic to be able to act as a binder for the fibre and form a firelog. A mixture of fibre material and saturated non-petroleum wax usually cannot be extruded.
Instead, a saturated wax is generally blended with an unsaturated wax in order to form a wax blend which has the necessary binding properties to allow a firelog to be formed. EP2104727 gives an example of this, and requires a wax component which is solid at room temperature, i.e. a saturated compound, in a blend with a wax component which is not solid at room temperature, i.e. an unsaturated compound.
Since at the moment the wax component of a firelog generally contains an unsaturated component, which does not burn as cleanly as a saturated component and/or contains petroleum waxes, firelogs are not as environmentally friendly as is desirable. Many do not pass the UK smokeless test for use in a Smoke Controlled Area. The firelogs that do pass this test, which are currently on the market, contain a very carefully blended wax component consisting of expensive “clean” saturated waxes, along with some “dirty” unsaturated waxes which are necessary to ensure the necessary binding properties of the wax components, for formation for the firelog.
There is a need for firelogs that burn more cleanly, in order to better meet environmental concerns.
In addition to open fires, many households have closed stoves, such as wood burning stoves. The popularity of such stoves has increased greatly in recent years. Firelogs are generally not suitable for use in stoves because the firelog itself would not retain its integrity in the intense heat. In a stove environment a conventional firelog would slump, causing a large flare-up. This creates a safety issue, as such uncontrolled flames are very dangerous. It would be advantageous to create a firelog which had sufficient integrity on burning to make it suitable for use in a stove.